Semiconductor device and method of manufacturing the same

ABSTRACT

In a method of obtaining a crystalline silicon film having high crystallinity at a low temperature and for a short time by using a catalytic element and using both a heat treatment and irradiation of laser light, a catalytic element which does not require a gettering step is used as the catalytic element for facilitating crystallization, so that a semiconductor device having high characteristics and high productivity is obtained. Specifically, a coating film of an element in group 14, such as germanium, which is the same group of the periodic table as silicon is formed on an amorphous silicon film formed on a glass substrate, a heat treatment at 550° C. for 4 hours is carried out, and further, irradiation of laser light is carried out, so that a crystalline silicon film is obtained. In the above structure, the element in group 14, which does not have a bad influence on TFT characteristics even if the element is left in the silicon film, is used, so that the semiconductor device having high characteristics and high productivity can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device using asemiconductor having crystallinity and a method of manufacturing thesame.

2. Description of the Related Art

A thin film transistor (hereinafter referred to as a TFT) using a thinfilm semiconductor is known. This TFT is constructed in such a mannerthat a thin film semiconductor is formed on a substrate and this thinfilm semiconductor is used. Although this TFT is used for various kindsof integrated circuits, the TFT receives attention especially as acomponent of an electrooptical device, especially as a switching elementprovided in each pixel and a driver element formed in a peripheralcircuit portion of an active matrix type liquid crystal display device.

As a thin film semiconductor used for the TFT, although it is easy touse an amorphous silicon film, there is a problem that its electricalcharacteristics are low. For the purpose of obtaining the improvement inthe characteristics of the TFT, it is appropriate that a silicon thinfilm having crystallinity is used. A silicon film having crystallinityis referred to as polycrystalline silicon, polysilicon, microcrystallinesilicon, or the like. In order to obtain the silicon film having thecrystallinity, it is appropriate that an amorphous silicon film is firstformed, and then, the film is crystallized by heating.

However, in crystallization by heating, it is necessary to carry outheating at a temperature of 600° C. or higher and for 10 hours or more,so that there is a problem that it is difficult to use a glass substrateas a substrate. For example, Corning 7059 glass used for an active typeliquid crystal display device has a glass distortion point of 593° C.,and there is a problem in heating at a temperature of 600° C. or higherwhen enlarging the area of a substrate is taken into consideration.

According to the study of the present inventors, it has been found thatif heating is carried out after a very small amount of element, such asnickel or palladium, is deposited on the surface of an amorphous siliconfilm, the amorphous film can be crystallized at a temperature of 550° C.for a processing time of about 4 hours. However, if a large amount ofelements as set forth above exist in the semiconductor, the reliabilityor electrical stability of a device using such semiconductor is damaged,and this is not preferable.

That is, although an element for facilitating crystallization, such asnickel, (in this specification, an element for facilitatingcrystallization will be referred to as a catalytic element) is necessarywhen an amorphous silicon film is crystallized, it is desirable not tomake the element contained in crystallized silicon to the utmost.Although various methods for gettering the catalytic element incrystallized silicon have been investigated to achieve this object, anymethod increases the number of steps for gettering and is not verypreferable in manufacturing a component.

Although it has been found that when the catalytic element isintroduced, crystallization can be made at a temperature of 600° C. orlower for a short time, the crystallinity obtained by the heat treatmenthas a limit, and there occurs a problem that the crystallinity becomesinsufficient.

SUMMARY OF THE INVENTION

An object of the present invention is, in manufacture of a thin filmsilicon semiconductor having crystallinity by a heat treatment at atemperature of 600° C. or lower using a catalytic element, to satisfythe requests of (1) obtaining a method with high productivity bydecreasing the number of steps, and (2) obtaining crystallinity higherthan that obtained by the heat treatment.

According to the present invention, in order to achieve the aboveobject, the following means are used so that a silicon film havingcrystallinity is obtained.

A heat treatment is carried out while a simple substance of a catalyticelement for facilitating crystallization of an amorphous silicon film ora compound containing the catalytic element is made to be retained onthe amorphous silicon film, so that a part or all of the amorphoussilicon film is crystallized. Then, the film is irradiated with laserlight or intense light so that crystallization is further promoted. Akind of or plural kinds of elements selected from group 14 of theperiodic table are used as the above catalytic element.

Especially, the present invention has a feature that a kind of or pluralkinds of elements selected from group 14 which is the same as the groupof the periodic table to which silicon of semiconductor materialbelongs, are used as the catalytic element. That is, when the element ingroup 14 is used as the catalytic element, a gettering step becomesunnecessary. This is because, in general, elements which belong to thesame group have similar properties to each other, and even if thecatalytic element in group 14 remains in a silicon film in group 14,deterioration of semiconductor characteristics does not occur. That thecharacteristics are not deteriorated is obvious also from the fact thata group 14—group 14 alloy semiconductor, such as SiGe or SiSn, is knownas a compound alloy semiconductor.

It is preferable to use a kind of or plural kinds of elements selectedfrom germanium, tin, and lead as the catalytic element. Although carbon,germanium, tin and lead are known as elements in group 14 other thansilicon, among the elements, each of germanium, tin, and lead haselectronegativity similar to that of silicon, and those elements aremixed at random. Thus, when those elements are used, the semiconductorcharacteristics are improved as compared with the case where carbon isused.

It is further preferable to use germanium as the catalytic element.Silicon and germanium are similar to each other in not onlyelectronegativity but also covalent radius, and a random network ofcontinuous and uniform composition is formed, so that the semiconductorcharacteristics are further improved as compared with the case where tinor lead is used.

Another feature of the present invention is that after a part or all ofthe amorphous silicon film is crystallized by carrying out the heattreatment, the film is irradiated with laser light or intense light tofurther promote crystallization. By this method, a crystalline siliconfilm having extremely excellent crystallinity can be obtained through amethod with high productivity.

By carrying out the irradiation of laser light after the heat treatment,the crystallinity of the silicon film crystallized by the heat treatmentcan be further improved. In the case where crystallization is partiallycaused by the heat treatment, the crystal growth is further progressedfrom the portion which is irradiated with laser light so that the stateof higher crystallinity can be realized.

For example, in the case where an introduction amount of catalyticelement is small, crystallization occurs in minute scattered regions.This state can be said a state in which crystalline constituents andamorphous constituents are mixed with each other on the whole. Here, byirradiation of laser light, crystal growth can be made from crystalnuclei existing in the constituents having crystallinity, so that thesilicon film having high crystallinity can be obtained. That is, a smallcrystal grain can be grown into a large crystal grain. Like this, theeffect of promoting crystallinity by irradiation of laser light becomesnotable especially in the case of a silicon film where crystallizationis incomplete.

Instead of irradiating laser light, a method of irradiation of intenselight, especially infrared light may be adopted. Since infrared light isnot easily absorbed by glass, but is easily absorbed by a silicon thinfilm, it can selectively heat a silicon thin film formed on a glasssubstrate and is useful. This method of using infrared light is calledrapid thermal annealing (RTA) or rapid thermal process (RTP).

Like this, a kind of or plural kinds of elements selected from elementsin group 14, preferably a kind of or plural kinds of elements selectedfrom germanium, tin, and lead, more preferably, germanium is made to beretained on an amorphous silicon film, and a heat treatment is carriedout, and then, the film is irradiated with laser light or intense light,so that a crystalline silicon film having excellent crystallinity can beobtained. In the characteristics of a semiconductor using thiscrystalline silicon film, an increase or unevenness of off current isnot seen, and a device having excellent characteristics can be obtainedeven if the catalytic element is not gettered.

Moreover, the present invention has a feature that an active region of asemiconductor device having at least one of PN, PI, NI and otherelectric junctions is formed by using a crystallized crystalline siliconfilm. As the semiconductor device, a thin film transistor (TFT), adiode, and a photosensor can be used.

By adopting the structure of the present invention, the basic effectsdescribed below can be obtained.

(a) A crystalline silicon film having excellent crystallinity can beobtained without requiring a high temperature process.

(b) It is not necessary to getter a catalytic element, so that devicemanufacturing steps can be greatly reduced.

(c) Since a catalytic element may remain in a silicon film, it is notnecessary to precisely control the amount of introduction of thecatalytic element.

(d) Since crystallization is further promoted by irradiation of laserlight or intense light, a crystalline silicon film having extremelyexcellent crystallinity can be obtained.

As a method of introducing a catalytic element for facilitatingcrystallization, a plasma treatment, a vapor phase method such as an ionimplantation method, a solid phase method, or a solution applying methodis used. The solid phase method is a method in which a film containing acatalytic element is formed by using a plasma CVD method, an LPCVDmethod, a PVD method, or the like, and annealing is carried out todiffuse the catalytic element so that the catalytic element isintroduced. The solution applying method is a method of applying asolution in which a simple substance of a catalytic element or acompound containing a catalytic element is dissolved or dispersed. Forexample, in the case where germanium is used as the catalytic element,as the compound containing the catalytic element, it is possible to usegermanium bromide, germanium chloride, germanium iodide, germaniumoxide, germanium sulphide, germane, germane acetate, tris(2,4-pentanedionate) germanium perchlorate, tetramethylgermane,tetraethylgermane, tetraphenylgermane, hexaethyl germanium, or the like.

In a method of applying a solution containing an element forfacilitating crystallization to an amorphous silicon film, it ispossible to use an aqueous solution, an organic solvent solution, or thelike as the solution. Here, the term “containing” means both cases thatthe element is contained as a compound and the element is containedmerely by dispersion.

As the solvent containing the catalytic element, it is possible to useone selected from the group consisting of polar solvents of water,alcohol, acid, and ammonium, and non-polar solvents of benzene, toluene,xylene, carbon tetrachloride, chloroform, and ether.

It is also effective to add a surfactant in the solution containing thecatalytic element. This is for increasing adhesiveness to a coatedsurface and controlling adsorption. The surfactant may be applied to thecoated surface in advance.

In the case where a simple substance of germanium is used as thecatalytic element, it is necessary to dissolve the substance in an acidto form a solution.

Although the above are examples using a solution in which the catalyticelement is completely dissolved, even if the catalytic element is notcompletely dissolved, it is also possible to use a material likeemulsion in which a simple substance of the catalytic element or powdermade of a compound containing the catalytic element is uniformlydispersed in a dispersion medium. Alternatively, a solution for formingan oxide film may be used. As such a solution, it is possible to use OCD(Ohka Diffusion Source) made by Tokyo Ohka Kogyo Corp. If this OCDsolution is used, a silicon oxide film can be easily formed by applyingit onto the formed surface and baking at about 200° C. Moreover, sinceimpurities can be freely added, the solution can be used for the presentinvention.

When the catalytic element is selectively retained, crystal growth canbe selectively carried out. Especially in this case, it is possible tocause crystal growth in the direction almost parallel to the surface ofa silicon film from the region where the catalytic element has beenretained to the region where the catalytic element has not beenretained. This crystal growth in the direction almost parallel to thesurface of a silicon film will be referred to as lateral growth in thisspecification.

If a device is manufactured in such a way that the direction of crystalgrain boundaries in the lateral growth is almost coincident with themoving direction of carriers, an active layer region of thesemiconductor device along the moving direction of carriers becomes aregion where grain boundaries hardly exist or a region where uniformgrain boundaries exist, so that the mobility of carriers is improved,dispersion among components disappears, and reliability of the deviceincreases. Thus, it is effective in device manufacture to form an activelayer region of a semiconductor device by using the region where crystalgrowth has been made in the lateral direction.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1E are views showing manufacturing steps according to anembodiment;

FIGS. 2A to 2E are views showing manufacturing steps according to anembodiment;

FIGS. 3A to 3F are views showing manufacturing steps according to anembodiment;

FIGS. 4A to 4D are views showing manufacturing steps according to anembodiment;

FIG. 5 is a view showing a structure of a liquid crystal module; and

FIGS. 6A to 6F are views showing structures of electronic equipments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the drawings.

Embodiment 1

This embodiment shows an example in which a TFT is obtained by using acrystalline silicon film which is manufactured by retaining a catalyticelement in group 14 for facilitating crystallization on an amorphoussilicon film, crystallizing the amorphous film by heating, and furtherimproving the crystallinity of the film by irradiation of laser light.The TFT of this embodiment can be used for a driver circuit and a pixelportion of an active matrix type liquid crystal display device. It isneedless to say that an applied scope of the TFT is not limited to theliquid crystal display device but the TFT can be applied to a commonthin film integrated circuit.

FIGS. 1A to 1E schematically show manufacturing steps of thisembodiment. In this embodiment, Corning 7059 glass is used for a glasssubstrate 301. First, a silicon oxide film 302 as an under film with athickness of 200 nm is formed on the glass substrate 301. This siliconoxide film 302 is provided to prevent impurities from diffusing from theglass substrate.

Then an amorphous silicon film 3030 with a thickness of 10 to 150 nm isformed by a plasma CVD method or an LPCVD method. Here, the amorphoussilicon film with a thickness of 50 nm is formed by the LPCVD method.

Then a germanium film 304 with a thickness of 5 to 100 nm, preferably 10to 50 nm is formed by the LPCVD method using GeH₄ as a raw material(FIG. 1A). Then a heat treatment in a heating furnace is carried out ina nitrogen atmosphere at 550° C. for 4 hours. As a result, it ispossible to obtain a crystalline silicon thin film 3031 formed on thesubstrate 301.

Although the above heat treatment can be carried out at a temperature of450° C. or higher, if the temperature is low, a heating time must beprolonged, so that production efficiency is lowered. On the other hand,if the temperature is made 600° C. or higher, a problem of heatresistance of the glass substrate used as the substrate occurs.

By carrying out the above heat treatment, the silicon film in which anamorphous constituent and crystal constituent are mixed is obtained. Thecrystal constituent is a region where crystal nuclei exist. Thereafter,the germanium film is removed, and the silicon film 3031 is irradiatedwith several shots of a KrF excimer laser (wavelength 248 nm, pulsewidth 30 nsec) in a nitrogen atmosphere at a power density of 200 to 350mJ/cm², so that the crystallinity of the silicon film 3031 is promoted.In the irradiation step of the laser light, the substrate may be heatedup to about 400° C. By this step, crystal growth is made using crystalnuclei existing in the crystal constituent as nuclei. This step may becarried out by the foregoing irradiation of infrared light (FIG. 1B).Next, the crystallized silicon film is patterned to form an island-likeregion 3032. This island-like region 3032 forms an active layer of theTFT. Then a silicon oxide film 305 with a thickness of 20 to 150 nm,here 100 nm is formed. This silicon oxide film functions also as a gateinsulating film (FIG. 1C).

Care must be paid to the manufacture of the above silicon oxide film305. Here, TEOS was used as a raw material, and was decomposed anddeposited, together with oxygen, by an RF plasma CVD method at asubstrate temperature of 150 to 600° C., preferably 300 to 450° C. Apressure ratio of TEOS to oxygen was made 1:1 to 1:3, the pressure wasmade 0.05 to 0.5 torr, and the RF power was made 100 to 250 W.Alternatively, the silicon oxide film was formed by a low pressure CVDmethod or an atmospheric pressure CVD method using TEOS, together withan ozone gas, as a raw material at a substrate temperature of 350 to600° C., preferably 400 to 550° C.

In this state, the crystallization of the silicon region 3032 may bepromoted by irradiation of KrF excimer laser light (wavelength 248 nm,pulse width 20 nsec) or intense light comparable to the laser light.Especially, RTA (Rapid Thermal Annealing) using infrared light canselectively heat only silicon without heating a glass substrate, and candecrease interfacial levels at an interface between silicon and siliconoxide film, so that it is useful in manufacture of an insulated gatetype field effect semiconductor device.

Thereafter, a film having a thickness of 200 nm to 1 μm and containingaluminum as its main ingredient is formed by an electron beamevaporation method, and this film is patterned to form a gate electrode306. The film containing aluminum as its main ingredient may be dopedwith scandium (Sc) of 0.15 to 0.2 wt %. Next, the substrate is immersedin an ethylene glycol solution containing tartaric acid of 1 to 3% andhaving pH≈7, and anodic oxidation is carried out while using platinum asa cathode and the gate electrode of aluminum as an anode. The anodicoxidation is carried out in such a manner that voltage is first raisedup to 220 V at a constant current, this state is held for 1 hour, andthe oxidation is ended. In this embodiment, in a constant current state,it is appropriate that a rising speed of voltage is 2 to 5 V/min. Inthis way, an anodic oxide 307 with a thickness of 150 to 350 nm, forexample, 200 nm is formed (FIG. 1D). The anodic oxide has a function toelectrically and mechanically protect the surface of the film mainlycontaining aluminum which has low heat resistance. In this embodiment,although aluminum covered with anodic oxide is used for the gateelectrode, silicon or silicide having superior heat resistance may beused.

Thereafter, by an ion doping method (also called a plasma dopingmethod), an impurity (phosphorus) is implanted in the island-likesilicon film of each TFT by using the gate electrode portion as a maskin a self-aligning manner. Phosphine (PH₃) is used as a doping gas. Thedosage is made 1 to 4×10¹⁵ cm⁻². Further, by irradiation of KrF excimerlaser light (wavelength 248 nm, pulse width 20 nsec), crystallinity of aportion where crystallinity was deteriorated by introduction of theabove impurity is improved. The energy density of laser light is 150 to400 mJ/cm², preferably 200 to 250 mJ/cm². In this way, N-type impurity(phosphorus) regions 3132 and 3232 are formed. The sheet resistance ofthese regions was 200 to 800 Ω/□. In this step, so-called intense lightcomparable to the laser light, such as in the RTA, may be used insteadof using the laser light.

Thereafter, as an interlayer insulator 308, a silicon oxide film with athickness of 300 nm is formed on the whole surface by using TEOS as araw material and by a plasma CVD method using TEOS and oxygen, or a lowpressure CVD method or atmospheric CVD method using TEOS and ozone. Thesubstrate temperature is made 250 to 450° C., for example, 350° C.

Then the interlayer insulator 308 is etched to form contact holes insource/drain of the TFT, as shown in FIG. 1E, and source/drainelectrodes/wiring lines 3091 and 3092 made of aluminum or multilayerfilms of titanium nitride and aluminum are formed.

Finally, annealing in hydrogen is carried out at 300 to 400° C. for 1 to2 hours, so that hydrogenating of silicon is completed. In this way, theTFT is completed. A plurality of TFTs manufactured at the same time arearranged in matrix, so that an active matrix type liquid crystal displaydevice is completed. This TFT includes the source/drain regions3132/3232 and a channel formation region 3332. Portions 3100 and 3101become electrical junction portions of NI.

In the TFT manufactured in this embodiment, by using the catalyticelement in group 14, a mobility of not less than 150 cm²/Vs can beobtained for an N-channel TFT without a gettering step. It is alsoascertained that Vth is low and the TFT has excellent characteristics.Moreover, it is also ascertained that the dispersion of mobility iswithin ±10%. It is conceivable that the low dispersion is due to theincomplete crystallization by the heat treatment and the step ofpromoting the crystallinity by the irradiation of laser light. Althougha TFT having a mobility of not less than 150 cm²/Vs for an N-channel TFTcan be easily obtained in the case where only laser light is used, thedispersion is high and uniformity as in this embodiment can not beobtained.

In this embodiment, although a method of introducing a catalytic elementonto an amorphous silicon film has been described, a method ofintroducing the catalytic element into a portion under the amorphoussilicon film may be adopted. In that case, it is appropriate that aftera film containing the catalytic element is formed, the amorphous siliconfilm is formed. The method of introducing the catalytic element is notlimited to the LPCVD method, but another solid phase method, vapor phasemethod, solution applying method, or the like may be used.

Embodiment 2

This embodiment shows an example in which a TFT is obtained by using acrystalline silicon film which is manufactured by retaining a catalyticelement in group 14 for facilitating crystallization on an amorphoussilicon film by using a solution applying method, crystallizing theamorphous film by heating, and further improving the crystallinity ofthe film by irradiation of laser light. The TFT of this embodiment canbe used for a driver circuit and a pixel portion of an active matrixtype liquid crystal display device. It is needless to say that anapplied scope of the TFT is not limited to the liquid crystal displaydevice, but the TFT can be applied to a common thin film integratedcircuit.

FIGS. 2A to 2E schematically show manufacturing steps of thisembodiment. First, a silicon oxide film 402 as an under film with athickness of 200 nm is formed on a glass substrate 401 (Corning 7059).This silicon oxide film is provided to prevent impurities from diffusingfrom the glass substrate. Further, an amorphous silicon film 4030 with athickness of 20 to 150 nm, here, 50 nm is formed by a plasma CVD method.

After a hydrofluoric acid treatment for removing a natural oxide film iscarried out, a thin oxide film with a thickness of about 2 nm is formedby irradiation of UV light in an oxygen atmosphere. The manufacturingmethod of the thin oxide film may be a treatment with hydrogen peroxideor a method by thermal oxidation.

Then an acetate solution 404 containing germanium of 10 ppm (in weight)is applied (FIG. 2A), it is retained for 5 minutes, and spin drying iscarried out by using a spinner. Thereafter, a crystallized silicon film4031 is obtained by heating at 550° C. for 4 hours.

By carrying out the above heat treatment, a silicon film in which anamorphous constituent and a crystal constituent are mixed is obtained.The crystal constituent is a region where crystal nuclei exist.Thereafter, the germanium film is removed, and the silicon film isirradiated with KrF excimer laser light of 200 to 300 ml/cm², so thatthe crystallinity of the silicon film is promoted. In the irradiationstep of the laser light, the substrate may be heated up to about 400° C.By this step, crystal growth is made using crystal nuclei existing inthe crystal constituent as nuclei (FIG. 2B).

Next, the crystallized silicon film 4031 is patterned to form anisland-like region 4032. This island-like region 4032 forms an activelayer of the TFT. Then a silicon oxide film 405 with a thickness of 100nm is formed. This silicon oxide film functions also as a gateinsulating film (FIG. 2C).

Subsequently, by a sputtering method, a film having a thickness of 300to 800 nm, for example, 600 nm and containing aluminum as its mainingredient (containing scandium of 0.1 to 0.3 wt %) is deposited. Then,a gate electrode 406 is formed by a well-known photolithography method.Next, the substrate is immersed in an ethylene glycol solution (pH isadjusted to a neutral state by ammonia) of 3% tartaric acid, and acurrent is made to flow in the solution to raise a voltage up to 100 Vat a rate of 1 to 5 V/min, for example, 4 V/min so that anodic oxidationis carried out. At this time, not only the top surface of the gateelectrode but also the side of the gate electrode is subjected to anodicoxidation, and a dense nonporous anodic oxide 407 with a thickness of100 nm is formed. The withstand voltage of this anodic oxide is 50 V orhigher. In this embodiment, although aluminum covered with anodic oxideis used as the gate electrode, silicon or silicide having superior heatresistance may be used.

Next, by a plasma doping method, an impurity (phosphorus) is implantedin the island-like region 4032 of silicon by using the gate electrode asa mask. Phosphine (PH₃) is used as a doping gas, and the accelerationvoltage is made 5 to 30 kV, for example, 10 kV. The dosage is made1×10¹⁴ to 8×10¹⁵ cm⁻², for example, 2×10¹⁵ cm⁻² (FIG. 2D).

Thereafter, irradiation of laser light is carried out from the above,and laser annealing is carried out, so that the doped impurity isactivated. Subsequently, a silicon oxide film 408 with a thickness of600 nm is formed as an interlayer insulator by a plasma CVD method. Thenan ITO electrode which becomes a pixel electrode is formed. Further,contact holes are formed, and electrode/wiring lines 4091 and 4092 of asource region and drain region of the TFT are formed out of a metallicmaterial, for example, a multilayer film of titanium nitride andaluminum. Finally, annealing is carried out in a hydrogen atmosphere of1 atmospheric pressure at 350° C. for 30 minutes. Through the abovesteps, the thin film transistor is completed (FIG. 2E).

In the TFT manufactured in this embodiment, by using the catalyticelement in group 14, a mobility of not less than 150 cm²/Vs can beobtained for an N-channel TFT without a gettering step. It is alsoascertained that Vth is low and the TFT has excellent characteristics.Moreover, it is also ascertained that the dispersion of mobility iswithin ±10%. It is conceivable that the low dispersion is due to theincomplete crystallization by the heat treatment and the step ofpromoting the crystallinity by the irradiation of laser light. Althougha TFT having a mobility of not less than 150 cm²/Vs for an N-channel TFTcan be easily obtained in the case where only laser light is used, thedispersion is high and uniformity as in this embodiment can not beobtained.

In this embodiment, although a method of introducing a catalytic elementonto an amorphous silicon film, a method of introducing a catalyticelement into a portion under the amorphous silicon film may be adopted.In that case, it is appropriate that after a film containing a catalyticelement is formed, the amorphous silicon film is formed. A method ofintroducing a catalytic element is not limited to the solution applyingmethod, but a solid phase method, a vapor phase method, a solutionapplying method using another solution, or the like may be used.

Embodiment 3

This embodiment shows an example in which germanium is selectivelyintroduced, and an electronic device is formed by using a region wherecrystals grow in a lateral direction (direction parallel to a substrate)from a portion where germanium has been introduced. In the case wheresuch a structure is adopted, the crystallinity in an active layer regionof the device can be increased, so that it is possible to make astructure extremely desirable in view of electrical stability andreliability of the device.

FIGS. 3A to 3F show manufacturing steps of this embodiment. First, asubstrate 201 (Corning 7059, 10 cm square) is washed, and an under film202 of silicon oxide with a thickness of 200 nm is formed by using a rawmaterial gas of TEOS (tetra ethoxy silane) and oxygen by plasma CVD.Then an amorphous silicon film 203 with a thickness of 50 to 150 nm, forexample, 100 nm is formed. Next, a silicon oxide film 205 with athickness of 50 to 200 nm, for example, 100 nm is subsequently formed bya plasma CVD method. Then the silicon oxide film 205 is selectivelyetched to form a region 206 where amorphous silicon is exposed.

Then a germanium film with a thickness of 5 to 100 nm, preferably 10 to50 nm is formed by an LPCVD method using GeH₄ as a raw material.Thereafter, heat annealing is carried out in a nitrogen atmosphere at500 to 600° C., for example, 550° C. for 4 hours, so that the siliconfilm 203 is crystallized. The crystal growth progresses in the directionparallel to the substrate as indicated by an arrow from the region 206,where germanium is in contact with the silicon film, as a startingpoint. In the drawing, a region 204 is a portion which is crystallizedthrough direct introduction of germanium and the region 203 indicates aportion which is crystallized in the lateral direction. The size of thecrystal in the lateral direction indicated by 203 is about 25 to 100 μm.It is ascertained that the direction of crystal growth is roughly in a<111> axis direction (FIG. 3A).

After the crystallizing step by the above heat treatment, thecrystallinity of the silicon film 203 is further promoted by irradiationof infrared light. This step is carried out by irradiation of infraredlight with a peak at a wavelength of 0.6 to 4 μm, for example, 0.8 to1.4 μm. By this step, it is possible to obtain effects comparable tothose obtained by a high temperature heat treatment for several minutes.

A halogen lamp is used as a light source of infrared light. Theintensity of infrared light is adjusted so that the temperature of amonitor of a single crystal silicon wafer is between 900 and 1200° C.Concretely, the temperature of a thermocouple buried in the siliconwafer is monitored, and the monitoring result is fed back to the lightsource of infrared light. In this embodiment, a temperature rise isconstant and its rate is 50 to 200° C./second, and a temperature fall isnatural cooling and its rate is 20 to 100° C./sec. Since thisirradiation of infrared light selectively heats the silicon film,heating to the glass substrate can be suppressed to the minimum.

Next, the silicon oxide film 205 is removed. At this time, an oxide filmformed on the surface of the region 206 is also removed at the sametime. Then, after the silicon film 204 is patterned, dry etching iscarried out, so that an island-like active layer region 208 is formed.At this time, the region denoted by 206 in FIG. 3A is a region wheregermanium is directly introduced, and germanium with a highconcentration exists. It is ascertained that germanium with a highconcentration exists also at the end of the crystal growth. Even ifgermanium with a high concentration exists in the silicon film, it doesnot affect the semiconductor characteristics. However, if theconcentration of germanium in the active region is irregular, thecharacteristics of components become irregular, which is not preferable.Thus, this embodiment adopts such a structure that the region where theconcentration of germanium is high in the active layer 208 does notoverlap with a channel formation region.

Thereafter, the active layer is left as it is for one hour in anatmosphere containing water vapor of 100 vol %, and having 10atmospheric pressures and a temperature of 500 to 600° C., typically550° C., so that the surface of the active layer (silicon film) 208 isoxidized to form a silicon oxide film 209. The thickness of the siliconoxide film is made 100 nm. After the silicon oxide film 209 is formed bythermal oxidation, the substrate is held in an ammonia atmosphere (1atm., 100%) at 400° C. Then, the substrate in this state is irradiatedwith infrared light having a peak at a wavelength of 0.6 to 4 μm, forexample, 0.8 to 1.4 μm for 30 to 180 seconds, and a nitriding treatmentis applied to the silicon oxide film 209. At this time, HCl of 0.1 to10% may be mixed in the atmosphere (FIG. 3B).

Subsequently, a film of aluminum (containing scandium of 0.01 to 0.2%)with a thickness of 300 to 800 nm, for example, 600 nm is formed by asputtering method. Then, the aluminum film is patterned to form a gateelectrode 210 (FIG. 3C).

Further, the surface of the aluminum is subjected to anodic oxidation,so that an oxide layer 211 is formed on the surface. This anodicoxidation is carried out in an ethylene glycol solution containingtartaric acid of 1 to 5%. The thickness of the obtained oxide layer 211is 200 nm. Incidentally, since the thickness of this oxide 211 becomes athickness forming an offset gate region in a subsequent ion doping step,the length of the offset gate region can be determined by the aboveanodic oxidation step (FIG. 3D). Silicon or silicide superior toaluminum in heat resistance may be used as the gate electrode. In thecase where the gate electrode is formed out of silicon or silicide, anoffset gate region can be formed by ion doping after a side wall isprovided on the gate electrode.

Next, by an ion doping method (also called a plasma doping method), animpurity (here, phosphorus) for giving N-type conductivity is added inthe active layer region (constituting source/drain, and channel) byusing a gate electrode portion, that is, the gate electrode 210 and theoxide layer 211 around the gate electrode as a mask in a self-aligningmanner. Phosphine (PH₃) is used as a doping gas, and the accelerationvoltage is made 60 to 90 kV, for example, 80 kV. The dosage is made1×10¹⁵ to 8×10¹⁵ cm⁻², for example, 4×10¹⁵ cm⁻². As a result, N-typeimpurity regions 212 and 213 can be formed. As is apparent from thedrawing, the impurity regions and the gate electrode make an offsetstate in which each of the impurity regions is apart from the gateelectrode at a distance of “x”. Such an offset state is effectiveespecially in lowering a leak current (also called an off current) whena reverse voltage (minus voltage in the case of an N-channel TFT) isapplied to the gate electrode. Particularly, in the TFT for controllinga pixel of an active matrix as in this embodiment, for the purpose ofobtaining an excellent picture image, it is desirable that the leakcurrent is low so that an electric charge stored in a pixel electrodedoes not escape. Thus, it is effective to provide an offset.

Thereafter, annealing is carried out by irradiation of laser light. Forthe laser light, although a KrF excimer laser (wavelength 248 nm, pulsewidth 20 nsec) is used, another laser may be used. The irradiationconditions of laser light are such that the energy density is 200 to 400mJ/cm², for example, 250 mJ/cm², and irradiation of 2 to 10 shots forone place, for example, 2 shots are made. The effect may be increased byheating the substrate up to about 200 to 450° C. at the irradiation ofthe laser light (FIG. 3E).

Subsequently, a silicon oxide film 214 with a thickness of 600 nm as aninterlayer insulator is formed by a plasma CVD method. Further, atransparent polyimide film 215 is formed by a spin coating method sothat the surface is flattened.

Then, contact holes are formed in the interlayer insulators 214 and 215,and electrode/wiring lines 217 and 218 of the TFT are formed out of ametallic material, for example, a multilayer film of titanium nitrideand aluminum. Finally, annealing at 350° C. for 30 minutes is carriedout in a hydrogen atmosphere of 1 atmospheric pressure, so that a pixelcircuit of an active matrix including the TFT is completed (FIG. 3F).

The crystallinity of the active region of the TFT manufactured by thisembodiment is excellent, so that the TFT can have a high mobility, andcan be used for a driver circuit of an active matrix type liquid crystaldisplay device.

Although germanium is used as the catalytic element in this embodiment,other elements in group 14 can also be used. Moreover, although theLPCVD method is used as the method of introducing germanium, even if amethod, such as a solid phase method using another method, a vapor phasemethod, or a solution applying method, is used, similar effects can beobtained.

Embodiment 4

In this embodiment, the present invention is applied to a reversestagger type TFT. FIGS. 4A to 4D are sectional views showingmanufacturing steps of this embodiment. First, an under film (not shown)of silicon oxide with a thickness of 200 nm is formed on a substrate(Corning 7059) 101 by a sputtering method. Then a gate electrode 102made of metal silicide is formed. Further, a gate insulating film 103 isformed.

Next, an intrinsic (I-type) amorphous silicon film with a thickness of50 to 150 nm, for example, 100 nm is formed by an LPCVD method. Then agermanium film with a thickness of 5 to 100 nm, preferably 10 to 50 nmis formed by the LPCVD method using GeH₄ as a raw material. The film iscrystallized by annealing in a nitrogen atmosphere (atmosphericpressure) at 550° C. for 4 hours. After the germanium film is removed,crystallization is further promoted by irradiation of KrF excimer laserlight. Then the silicon film is patterned to form an island-like siliconfilm (active layer of the TFT) 105 (FIG. 4B). Next, a mask 106 isprovided, and an impurity (here, phosphorus) for giving N-typeconductivity is added in an active layer region (constitutingsource/drain, and channel) by an ion doping method (also called a plasmadoping method). Phosphine (PH₃) is used as a doping gas, and theacceleration voltage is made 60 to 90 kV, for example, 80 kV. The dosageis made 1×10¹⁵ to 8×10¹⁵ cm⁻², for example, 5×10¹⁵ cm⁻². As a result,N-type impurity regions 107 and 108 are formed.

Thereafter, annealing is carried out by irradiation of laser light.Although a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) isused for the laser light, other lasers may be used. The irradiationconditions of laser light are such that the energy density is 200 to 400mJ/cm², for example, 250 mJ/cm², and irradiation of 2 to 10 shots forone place, for example, 2 shots is carried out. The effect may beincreased by heating the substrate up to about 200 to 450° C. at theirradiation of the laser light (FIG. 4C). This step may be a method bylamp annealing using near infrared light.

Next, as an interlayer insulating film, a silicon oxide film 112 and apolyimide film 113 are formed. Further, contact holes are formed, andmetal wiring lines of TFT 110 and 111 are formed out of a metallicmaterial, for example, a multilayer film of titanium nitride andaluminum. Finally, annealing is carried out in a hydrogen atmosphere of1 atmospheric pressure at 350° C. for 30 minutes so that the reversestagger type TFT is completed (FIG. 4D).

The mobility of the TFT obtained by the method described above was 110to 150 cm²/Vs, and the S value was 0.2 to 0.5 V/digit. A P-channel TFTwas also manufactured by a similar method in which boron was doped insource/drain regions. The mobility of the p-channel TFT was 90 to 120cm²/Vs, and the S value was 0.4 to 0.6 V/digit. As compared with thecase where a gate insulating film is formed by a well-known PVD methodor CVD method, the mobility increased by 20 percents or more and the Svalue decreased by 20% or more.

Also in view of reliability, the TFT manufactured in this embodimentshowed an excellent result comparable to a TFT manufactured by hightemperature oxidation at 1,000° C.

In this embodiment, although germanium is used as the catalytic element,other elements in group 14 can also be used. Moreover, in thisembodiment, although the LPCVD method is used as a method of introducinggermanium, even if a method, such as a solid phase method using anothermethod, a vapor phase method, or a solution applying method, is used,similar effects can be obtained. Moreover, in this embodiment, germaniumis introduced into the whole surface of the silicon film and thecrystalline silicon film is obtained, even if germanium is selectivelyintroduced into a part of the silicon film and the crystalline siliconfilm is obtained by lateral growth, similar effects can be obtained.

Embodiment 5

In FIG. 5, this embodiment shows an example in which an active matrixsubstrate having a structure of the embodiments 1 to 4 is used and aliquid crystal display device is constructed. FIG. 5 shows a portioncorresponding to the main body of the liquid crystal display device,which is also called a liquid crystal module.

In FIG. 5, reference numeral 501 denotes a substrate (any of quartz,silicon wafer, and crystallized glass may be used), 502 denotes aninsulating silicon containing film as an under film on which a pluralityof TFTs are formed out of semiconductor films manufactured in accordancewith the manufacturing steps of the present invention.

These TFTs constitute a pixel matrix circuit 503, a gate side drivingcircuit 504, a source side driving circuit 505, and a logic circuit 506on the substrate. An opposite substrate 507 is bonded to such an activematrix substrate. A liquid crystal layer (not shown) is put between theactive matrix substrate and the opposite substrate 507.

In the structure shown in FIG. 5, it is desirable that all sides of theactive matrix substrate except one side are made flush with the sides ofthe opposite substrate. By doing so, the number of pieces obtained froma large substrate can be effectively increased.

At the one side, a part of the opposite substrate is removed to expose apart of the active matrix substrate, and an FPC (Flexible Print Circuit)508 is attached thereto. As the need arises, an IC chip (semiconductorcircuit constituted by MOSFETs formed on a single crystal silicon) maybe mounted on this part.

Since the TFT having the active layer of the semiconductor thin filmmanufactured in the present invention has an extremely high operationspeed, it is possible to integrally form a signal processing circuitdriven at a high frequency of several hundreds MHz to several GHz on thesame substrate as a pixel matrix circuit. That is, the liquid crystalmodule shown in FIG. 5 realizes a system-on-panel.

Although this embodiment shows the case where the present invention isapplied to the liquid crystal display device, it is also possible toconstruct an active matrix type EL (electroluminescence) display deviceor the like. It is also possible to form an image sensor or the likeprovided with a photoelectric conversion layer on the same substrate.

Incidentally, like the foregoing liquid crystal display device, ELdisplay device, or image sensor, a device having a function forconverting an optical signal into an electric signal, or an electricsignal into an optical signal is defined as an electrooptical device.The present invention can be applied to any electrooptical device whichcan be formed by using a semiconductor thin film on a substrate havingan insulating surface.

Embodiment 6

In the present invention, it is possible to construct not only anelectrooptical device as shown in the embodiment 5 but also a thin filmintegrated circuit (or semiconductor circuit) with an integratedfunctional circuits. For example, it is also possible to construct anarithmetic circuit such as a microprocessor and a high frequency circuit(MMIC: Microwave Module IC) for a portable equipment.

Further, it is also possible to construct a VLSI circuit integrated intoan ultra high density state by constructing a semiconductor circuit of athree dimensional structure by actively using the merit of a TFT using athin film. Like this, a semiconductor circuit with very richfunctionality can be constructed by using the TFT of the presentinvention. Incidentally, in the present specification, the semiconductorcircuit is defined as an electric circuit for controlling and convertingelectric signals by using semiconductor characteristics.

Embodiment 7

In this embodiment, examples of electronic equipments (applied products)incorporating electrooptical devices or semiconductor circuits shown inthe embodiment 5 or embodiment 6 will be described with reference toFIGS. 6A to 6F. Incidentally, the electronic equipments are defined asproducts incorporating a semiconductor circuit and/or an electronicdevice.

As electronic equipments to which the present invention can be applied,a video camera, a still camera, a projector, a head mount display, a carnavigation system, a personal computer, a portable information terminal(mobile computer, portable telephone, PHS, etc.) and the like areenumerated.

FIG. 6A shows a portable telephone which is constituted by a main body2001, an audio output portion 2002, an audio input portion 2003, adisplay device 2004, an operation switch 2005, and an antenna 2006. Thepresent invention can be applied to the audio output portion 2002, theaudio input portion 2003, the display device 2004, and the like.

FIG. 6B shows a video camera which is constituted by a main body 2101, adisplay device 2102, an audio input portion 2103, an operation switch2104, a battery 2105, and an image receiving portion 2106. The presentinvention can be applied to the display device 2102, the audio inputportion 2103, the image receiving portion 2106, and the like.

FIG. 6C shows a mobile computer which is constituted by a main body2201, a camera portion 2202, an image receiving portion 2203, anoperation switch 2204, and a display device 2205. The present inventioncan be applied to the camera portion 2202, the image receiving portion2203, the display device 2205, and the like.

FIG. 6D shows a head mount display which is constituted by a main body2301, a display device 2302, and a band portion 2303. The presentinvention can be applied to the display device 2302.

FIG. 6E shows a rear type projector which is constituted by a main body2401, a light source 2402, a display device 2403, a polarizing beamsplitter 2404, reflectors 2405 and 2406, and a screen 2407. The presentinvention can be applied to the display device 2403.

FIG. 6F shows a front type projector which is constituted by a main body2501, a light source 2502, a display device 2503, an optical system2504, and a screen 2505. The present invention can be applied to thedisplay device 2503.

As described above, the scope of application of the present invention isextremely wide and the present invention can be applied to electronicequipments of any field. Moreover, the present invention can be appliedto any product as long as it requires an electrooptical device orsemiconductor circuit.

According to the present invention, a semiconductor device ismanufactured by using a crystalline silicon film which is obtained insuch a manner that a catalytic element in group 14 is introduced andcrystallization is made at a low temperature for a short time, andfurther, irradiation of laser light or intense light is carried out.Thus, a device having excellent characteristics can be obtained withhigh productivity.

Like this, by using a catalytic element which does not affect theelectrical characteristics of a TFT, a TFT having excellent electricalcharacteristics can be realized and a semiconductor device having highperformance can be realized by the TFT.

1. A method of manufacturing a semiconductor device, comprising thesteps of: forming a gate electrode over an insulating surface; forming agate insulating film over the gate electrode; forming a semiconductorfilm comprising amorphous silicon over the gate insulating film;applying a solution comprising a catalyst for facilitatingcrystallization of amorphous silicon film to form a film comprising thecatalyst on the semiconductor film comprising amorphous silicon;crystallizing the semiconductor film comprising amorphous silicon bycarrying out a heat treatment; removing said film comprising saidcatalyst from a surface of the semiconductor film after the heattreatment; promoting crystallinity by irradiation of laser light orintense light after removing said film comprising said catalyst; andadding an impurity to said semiconductor film to form at least oneimpurity region imparting one conductivity type in said semiconductorfilm after promoting crystallinity by irradiation of laser light orintense light, wherein a kind of or plural kinds of elements selectedfrom elements in group 14 are used as the catalyst.
 2. A method ofmanufacturing a semiconductor device, comprising the steps of: applyinga solution comprising a catalyst for facilitating crystallization ofamorphous silicon film to form a film comprising the catalyst on thesemiconductor film comprising amorphous silicon; crystallizing thesemiconductor film comprising amorphous silicon by carrying out a heattreatment; removing said film comprising said catalyst from a surface ofthe semiconductor film after the heat treatment; promoting crystallinityby irradiation of laser light or intense light after removing said filmcomprising said catalyst; adding an impurity to said semiconductor filmto form at least one impurity region imparting one conductivity type insaid semiconductor film after promoting crystallinity by irradiation oflaser light or intense light; and patterning said crystallizedsemiconductor film into at least one semiconductor island after removingsaid film comprising said catalyst, wherein a kind of or plural kinds ofelements selected from elements in group 14 are used as the catalyst. 3.A method of manufacturing a semiconductor device according to claim 1,wherein germanium is used as the catalyst.
 4. A method of manufacturinga semiconductor device according to claim 2, wherein germanium is usedas the catalyst.
 5. A method of manufacturing a semiconductor deviceaccording to claim 3, wherein the compound containing the catalyst is atleast one selected from the group consisting of germanium bromide,germanium chloride, germanium iodide, germanium oxide, germaniumsulphide, germane, germane acetate, tris (2,4-pentanedionate) germaniumperchlorate, tetramethylgermane, tetraethylgermane, tetraphenylgermane,and hexaethyl germanium.
 6. A method of manufacturing a semiconductordevice according to claim 4, wherein the compound containing thecatalyst is at least one selected from the group consisting of germaniumbromide, germanium chloride, germanium iodide, germanium oxide,germanium sulphide, germane, germane acetate, tris (2,4-pentanedionate)germanium perchlorate, tetramethylgermane, tetraethylgermane,tetraphenylgermane, and hexaethyl germanium.
 7. The method according toclaim 1, wherein said semiconductor device is a device selected from thegroup consisting of a video camera, a mobile computer, a portabletelephone, a head mount display and a projector.
 8. The method accordingto claim 2, wherein said semiconductor device is a device selected fromthe group consisting of a video camera, a mobile computer, a portabletelephone, a head mount display and a projector.